The organo-alkali-metallic compounds are often used as initiators in the industries to synthesize the copolymers composed of vinyl aromatics and conjugated dienes. Then the coupling agent is used for coupling these polymers to form linear or star-shaped copolymers. By adopting this kind of coupling polymerization method, the thermoplastic elastomers, e.g. styrene-butadiene-styrene (SBS) copolymer, styrene-isoprene-styrene (SIS) copolymer, hydrogenated styrene-ethylene-butene-styrene (SEBS) copolymer, hydrogenated styrene-ethylene-propylene-styrene (SEPS) copolymer, etc. There are several advantages for the coupling polymerization method. For examples, the segment size of the styrene and the low viscosity can be well controlled during the polymerization. Compared with the sequential process, the coupling polymerization method has the excellent stability and high efficiency.
However, there are several problems for past used coupling agents. For instance, the coupling agents in UK patent No. 1014999 contain halogen, which will reduce the effect of the anti-oxidant, and the gains of the polymers by using this kind of coupling agents are not transparent enough. Furthermore, the byproduct, alkali metal halide, generated during the coupling reaction results in the corrosion of the pipes, and poisons the bacteria in the wasted water during the wasted water treatment. Moreover, this kind of coupling agents containing halogen has been listed as toxic compounds, and its use has been prohibited in several countries. Therefore, some substituted non-halogen coupling agents are gradually being developed, e.g. the coupling agent, Rx—Si—(OR1)y, in U.S. Pat. No. 7,220,798, and the alkoxy silane coupling agent, Si(OR)4, in Taiwan patent application No. 200307698. However, the copolymers by using these coupling agents contain only 0-5 weight percent of four-arm copolymers. The products made by these polymers after the hydrogenation have low modulus and low tensile resistance due to the low content of the four-arm copolymers, and accordingly the industrial applications of these products are limited.
As the above mentioned, although there have been a lot of known coupling agents applicable to the copolymers composed of the monomers of vinyl aromatics and conjugated dienes, the silane coupling agents with the alkoxy and alkenyl functional groups in the present invention can solve the above mentioned problems. The coupled copolymers by using the silane coupling agent with the alkoxy and alkenyl functional groups disclosed in the present invention do not produce any halide byproduct, can reach the coupling efficiency of 60-95 weight percent, and contain the four-arm copolymers in a range of 10-30 weight percent. For the hydrogenated coupled copolymers, the ratio of the coupling efficiency after hydrogenation to that before the hydrogenation is higher than 0.7, and the ratio of the content of the four-arm copolymers after hydrogenation to that before hydrogenation is also higher than 0.7. It can be seen from the above that the coupled copolymers by using the silane coupling agent with the alkoxy and alkenyl functional groups disclosed in the present invention contain obviously much more four-arm copolymers than those by using the conventional alkoxy silane coupling agents no matter the hydrogenation reaction is introduced or not. The processed products made by the coupled copolymers of the present invention have higher mechanical modulus, can sustain higher strengths, and have wider applications in the industries. The silane coupling agents with the alkoxy and alkenyl functional groups disclosed in the present invention have higher coupling efficiency. The coupled copolymers made by these silane coupling agents have excellent stability, still maintain high coupling efficiency and high content of four-arm copolymers after the hydrogenation, and therefore can provide excellent rubber mechanical properties. The present invention is described below.